Braking control for mine hoist



Dec. 13, 1966 w. e. A. TRQLLOPE 3,291453 BRAKING CONTROL FOR MINE HOIST Filed June 8, 1965 4 Sheets-Sheet l INVENTOR.

WILL/AM 6. A. TIQQLLQPE BRAKING CONTROL FOR MINE HOIST Filed June 8, 1965 4 Sheets-Sheet 2 Fi s INVENTOR. 3f WILL/AM a. A. TROLLOPE Dec. 13, 1966 w. s. A. TRQLLOPE 2 BRAKING CONTROL FOR MINE HOIST Filed June 8, 1965 4 Sheets-Sheet 5 FLUID STORAGE TANK 55 INVENTOR. SOL H T WILL/AM 61A. TROLLOPE 72 Dec. 13, 1966 w. G. A. TROLLOPE 3,291,451

BRAKING CONTROL FOR MINE HOIST Filed June 8, 1965 4 Sheets-Sheet 4 82 INVENTOR.

5 WILL/AM A. IWOLLOPE United States Patent 3,291,451 BRAKING CONTROL FOR MINE HOIST William G. A. Trollope, Terrasse Vaudreuil, Quebec,

Qanada, assignor to Canadian lingersoll-Rand Company Limited, Montreal, Quebec, Canada, a corporation of Qanada Filed June 8, 1965, Scr. No. 462,176 14 Claims. (Cl. 254-135) This invention relates to hoist apparatus and has particular reference to the pro-vision of new and improved means for controlling the braking of a dmm hoist to provide the hoist load with a safe, reasonable rate of deceleration whatever the phase of hoist operation when the brakes thereof are applied.

Conventionally a single-drum hoist is provided with a primary brake which acts upon a brake path or disc associated with the drum to control the operation thereof. In a multi-drum hoist, such as a double-drum hoist, it is conventional to provide such a primary brake for each of the drums of the hoist.

When both of the drums of a double-drum hoist are in simultaneous operation, the hoist is in balance and the brakes on both of the drums are available to decelerate and stop the load on the hoist in an emergency. However, when one of the drums is declutched and only the other thereof is hauling a load, the hoist is out of balance and only one of these primary brakes is available to deoelerate and stop the hoist load in an emergency. Thus, in order to permit out-of-balance hoist operation, each of the hoist brakes must be capable in an emergency of safely decelerating and stopping a load traveling under the most severe hoist operating conditions. That is to say, each brake must individually be capable of safely decelerating and stopping a descending load traveling at an overspeed. In a single-drum hoist the single primary brake must, of course, be capable of safely decelerating and stopping such a load.

In addition to these primary brakes, safety regulations and good practice usually dictate that the hoist be provided with .a secondary or emergency brake capable of independently safely decelerating and stopping the load in the event of failure of the primary brakes.

However, as the :primary hoist brakes very rarely fail, the emergency brake of a conventional drum hoist often serves only to provide the hoist with substantially twice the emergency braking power required for safely decelerating and stopping the load. Thus, the deceleration rate of a load on a conventional drum hoist is frequently dangerously high and unsafe to passengers in the load.

For example, with a double-drum hoist operating outof balance wtih a descending load, it is conventional to set the hoist brakes to deceleratc the load at a rate of around five feet/second/seoond. With the load ascending such that the weights of the load and of the rope assist the hoist brakes, however, this brake setting will act upon the same load to decelerate it at a rate of the order of twenty feet/ second/ second. This latter deceleration rate is, of course, undesirable as it closely approximates the rate likely to injure passengers in the load.

An object of the present invention is to provide new and improved means for controlling the braking of a drum hoist to provide the load hauled thereby with a safe, reasonable rate of deceleration regardless of the phase of hoist operation in which the brakes thereof are applied.

Another object of the invention is to provide new and improved control means of the type set forth which reduces the rate of deceleration of the load when the load is traveling under conditions likely to produce an unreasonable or unsafe deceleration rate.

Another object is to provide new and improved con- 3,291,451 Patented Dec. '13, 1965 trol means of the type set forth which is adapted to reduce the rate of deceleration of the load on a single-drum hoist when the hoist brakes are applied while the load on the hoist is ascending.

Another object is to provide new and improved control means of the type set forth which is particularly adapted to reduce the rate of deceleration of the load on a multi-drum hoist, such as a double-drum hoist, when the brakes thereof are applied while the hoist is in balance or is out of balance with an ascending load.

Another object is to provide new and improved control means of the type set forth which reduces the deceleration rate of the load by delaying the operation of the hoist emergency brake until the hoist has been brought to rest by its primary brakes.

Other objects and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings. It will be understood that changes may be made in the details of construction and arrangement of parts shown and described as the preferred form of the invention has been given by way of illustration only. It will also be understood that, although the present invention has been hereinafter shown and described with primary reference to a doubledrum hoist, this application of the invention has been given by way of illustration only.

Referring to the drawings:

FIG. 1 is a partially broken away, end view of a doubledrum mine hoist which is constructed in accordance with the present invent-ion;

FIG. 2 is an elevational view of the mine hoist illustrated in FIG. 1;

FIG. 2A is an enlarged sectional view of the hoist emergency braking mechanism taken on line 2A2A of FIG. 2 looking in the direction of the arrows;

FIG. 3 is a schematic view illustrating the fluid release system of the brake mechanisms on the mine hoist of FIGS. 1 and 2;

FIG. 4 is a detailed schematic view of one of the valves of the fluid brake release system shown in FIG. 3; and

FIG. 5 is a schematic view of the hoist electrical system controlling the fluid brake release system shown in FIG. 3.

Referring more particularly to the drawings wherein similar reference characters designate corresponding parts throughout the several views, FIGS. 1 and 2 illustrate a double-drum mine hoist designated generally at 1'3 incl-ud-in'g a pair of hoist or cable drum-s A and B and a rotatably jonrnalled shaft 12 which is carried by a supporting means 10a. Each of the hoist drums A and B carries a circumferentially toothed ring clutch member 11 which is adapted to be engaged by a radially slidable clutch member 12a on the shaft 12 to rotate the hoist drums A and B with the shaft .12. The clutches 8 and 9 formed by the clutch members 12a and the clutch members 11 on the drums A and B, respectively, are each individually and selectively controlled by an electrical control means (not shown) to allow both balanced and unbalanced operation of the drum hoist 1;).

A driven gear 13 is carried by the shaft 12 and meshes with a driving or pinion gear 14 which is carried by a driving or pinion shaft 15. The pinion shaft 15 is adapted to receive rotation from an actuating means or motor 16 and transmits rotation through the meshing gears 13 and 14 to the shaft 12 and, thence, to the clutched hoist drum or drums A and B.

The cables 17 are wound around each of the hoist drums A and B in opposing relationship and are trained over the sheaves 18 and 19 which are positioned above the entrances of the shafts 20 and 21, respectively. The cables 17 carry the loads or cages 22 and 23 that are hauled by the drums A and B in the shafts 20 and 21,

respectively. The cages 22 and 23 are movable within the shafts 20 and 21 within the vertical limits determined by the cage stops 20a.

Each of the hoist drums A and B is provided with a primary braking mechanism comprising a pair of brake shoes 24 and 25 having braking surfaces 26 adapted for frictional engagement with a braking surface 27 on the drums A and B. The brake shoes 24 and 25 on each of the drums A and B are positioned on opposite sides thereof and rock upon the links 28 which are supported by the bearings 29 seated upon the foundation 30 for the drum hoist 10.

Braking movement is transmitted between the brake shoes 24 and 25 by linkage means such as the bell cranks 31 and 32 which are pivotally connected to the upper and lower ends of the brake shoes 24 and have arms 33 pivotally connected to turnbuckles 34 connected the brake shoes 25. Brake controlling movement is transmitted to the bell cranks 31 and 32 by the links 35 and 36 which are pivotally connected to the free ends 37 of the bell cranks 31 and 32 and to a rocker arm 38 mounted upon a pivot 39 supported by the plate 40. The links 35 and 36 are connected to the rocker arm 38 on opposite sides of the pivot 39.

Each of the hoist drums A and B is provided with a fluid actuated motor for effecting movement of the brake shoes 24 and 25. For the purposes of illustration, a pneumatically actuated motor 41 comprising a cylinder 42 and a piston 43 has been shown for effecting this movement. It will be understood, however, that alternatively the motors 41 could be hydraulically operated.

As illustrated, the piston 43 of each of the pneumatic motors 41 is provided with an extension rod which extends through the upper end of the cylinder 42 and is connected to the free end of the rocker arm 38. The extension rods 44 serve to transmit movement of the pistons 43 into movement of the before-described braking mechanism. In the operation of this braking mechanism, more specifically, when pressurized fluid is supplied to the lower portion of one of the cylinders 42, the piston 43 therein is urged upwardly to actuate the link means of the braking mechanism and release the brake shoes 24 and 25 from the hoist drum A or B associated therewith. In other words, as illustrated, the brake shoes 24 and 25 automatically lock the hoist drums A and B against rotation unless released therefrom by the pneumatic motors 41.

An emergency or secondary braking mechanism designated generally at 45 is provided to insure the braking of the drum hoist in the event of failure of the beforedescribed primary hoist braking mechanism. As illustrated, the secondary braking mechanism 45 is operatively connected to the pinion shaft and automatically acts thereon, unless released, to brake the hoist drums A and B.

As will be seen from FIG. 2A, the secondary braking mechanism 45 comprises a pair of braking shoes 46 having surfaces 46a adapted for frictional engagement with a braking surface 47 circumferentially around the pinion shaft 15. As illustrated, pneumatic motor 48 which comprises a cylinder 49 and a piston 50 operatively carries the braking shoes 46 through the extension 51 of the piston 50 and the linkage arms 52 which are pivotally conected at 52a to the extension 51 and at 52b to the housing 53 of the secondary braking mechanism 45. The pneumatic motor 48, as will be seen from FIG. 2A, urges the braking surfaces 46a of the braking shoes 46 out of engagement with the braking surface 47 on the pinion shaft 15 to release the secondary braking mechanism 45 from the pinion shaft 15 upon extension of the piston 50 from the cylinder 49. It will be understood that, if desired, the motor 48 could be hydraulically actuated.

Although the primary and secondary braking mechanisms are, thus, illustrated as being of the shoe type, it will be understood that such have been so shown for the purposes of illustration only. The present invention is applicable to all forms of pressure released brake mechanisms whatever their type and regardless of whether the brake mechanisms are applied by means of weight, springs, fluid pressure or any combination thereof.

FIG. 3 schematically illustrates the pneumatic release system which supplies air or other suitable fluid under pressure to the pneumatic motors 41 and 48 for releasing the primary braking mechanisms from the hoist drums A and B and the secondary braking mechanism 45 from the pinion shaft 15. It will be understood that the pneumatic release system shown in FIG. 3 has been simplified for the purposes of brevity and clarity of description by the omission of pilot air lines in those instances in which the illustrated solenoid valves are solenoid pilot operated. Furthermore, it will be understood that the braking mechanisms have been shown in FIG. 3 in their engaged or locking positions. However, from this illustration of the braking mechanisms, the releasing thereof will be apparent to those skilled in the art in view of the following description.

As illustrated, pressurized air or other suitable pressurized fluid flows through the fluid line 54 from a fluid source (not shown) and is stored in the fluid storage tank 55. Upon actuation of the manual control valve 56, this pressurized fluid passes through the fluid line 57 and the control valve 56 and, assuming that the drum hoist 10 is in balanced operation and that the solenoid valves 58 and 59 are energized, passes through the fluid lines 60 and 61 to the cylinders 42. This pressurized fluid works in the cylinders 42 to extend the pistons 43 and, through the before-described linkage, releases the brake shoes 24 and 25 from the hoist drums A and B. If an emergency occurs requiring immediate braking of the hoist drums A and B, the solenoid valves 58 and 59 are de-energized as will be hereinafter shown and the fluid in the cylinders 42 exhausts through the exhaust passages 62 and 63 such that the braking mechanism is automatically set on the hoist drums A and B.

Thus, the hoist operator is normally able to control the force of the brake shoes 24 and 25 upon the hoist drums A and B by means of the control valve 56 which controls the flow of pressurized fluid to the cylinders 42. It will be seen that maximum braking force is transmitted to the hoist drums A and B when the control valve 56 is closed and/or the solenoids 58 and 59 are de-ener-gized. It will also be seen that the larger the quantity of pressurized fluid permitted through the control valve 56, the lower the braking force upon the hoist drums A and B.

During unbalanced operation of the drum hoist 10, it will be seen that the braking mechanism on the deolutched hoist drum may not be released by operation of the control valve 56. For example, assuming that the hoist drum A is 'declutched, the solenoid valve 58 would be de-energized. Thus, the control valve 56 would only direct fluid flow to the braking mechanism upon the engaged hoist drum B and would be unable to release the braking mechanism upon the disengaged hoist drum A.

The secondary braking mechanism 45 on the pinion shaft 15 is released by the pressurized fluid in the illustrated pneumatic release system independently of the control valve 56. More specifically, the cylinder 49 of the secondary braking mechanism 45 is directly connected to the fluid storage tank '55 and receives pressurized fluid therefrom through the fluid lines 57 and 64 and, depending upon the status of the solenoid valve 65, through either the fluid line 66, the solenoid valves 65 and 67, and the fluid line 68 or directly through the solenoid valve 65 and the fluid line 68. Exhausting of the cylinder 49 is accomplished through the fluid lines 68 and 66, the solenoid valves 65 and 67, and the exhaust passage 69.

As will be hereinafter shown, the solenoid valve 67 is continuously energized throughout the normal operation of the drum hoist 10. The solenoid valve 65, as

will also be hereinafter shown, is energized only if the drum hoist is in balanced operation or is in unbalanced operation with an ascending load. In other words, the solenoid valve 65 is not energized if the drum hoist 10 is operating out of balance with a descending load. However, in the event of a necessary emergency stop of the drum hoist 10', both solenoid valves 65 and 67 are deenergized to permit application of the secondary braking mechanism 45.

The solenoid valve 65 is constructed such that, when energized, it delays application of the secondary braking mechanism 45 on the pinion shaft until after the drum hoist 10 has been braked by the primary braking mechanism thereon. Thus, as the solenoid valve 65 is only energized when the drum hoist It) is in balanced operation or is, alternatively, in out-of-balance operation with an ascending load, it will be seen that this delay in the application of the secondary braking mechanism may only occur when the drum hoist llli is braked under these circumstances. Conversely, as the solenoid valve is not energized when the drum hoist 10 is unbalanced and is hautlin-g a descending load, it will be seen that the solenoid valve 65 will not delay application of the secondary braking mechanism 45 in this circumstance.

More specifically, the solenoid valve 65 includes a builtin time delay or lapse which prevents immediate movement of the valve 6-5 to its dc-energized state upon deenergizati-on thereof. This time delay is preferably independent of the electrical apparatus of the drum hoist 10 as the application of the braking mechanism 45 may be necessitated by a failure of electrical power. In practice, it has been found that a valve with a built-in pneumatic time delay is usually preferable for use as the solenoid valve 65 and that a time delay of three to four seconds is ordinarily suitable. The solenoid valve 67 is adapted to instantaneously respond to both energization and de-energization signals.

FIG. '4 illustrates schematically the details of construction of one form of a valve having a built-in time delay which is suitable for use as the solenoid valve 65 when the fluid employed as the working medium is a compressible fluid such as, for example, compressed air. It Wllll be understood that this valve has been shown for the purposes of illustration only and that other forms of solenoid valves having built-in time delays may alternatively be used.

The valve illustrated in FIG 4 comprises a fluid actuated primary valve 70 which is returned by a spring 71 and communicates the fluid ,lines 64 and 66 with the fluid line 68 to the cylinder 49. The solenoid '72 of the illustrated solenoid valve 65 controls a spring returned pilot valve 73 to control fluid passage thnough the fluid lines 74 and which lead to the pilot fluid supply (not shown) and exhaust, respectively. Energization oi the solenoid 72 effects movement of the spring returned pilot valve 73 to connect the fluid line 74 with the fluid cylinder 70a of the primary valve 70 through the check valve 75a, the restriction valve 76, and the receiver 77. As no unnecessary time delay is desired in the movement of the primary valve 70 upon energization of the solenoid 72, the restriction valve 76 is opened to its maximum open position. When the solenoid 72 is de-ene-rgized, the fluid in the receiver 77 and in the fluid cylinder 79a leaks away to exhaust through the restriction 78 and the check valve 79, the restriction valve 78 being set to restrict such fluid passage to delay the return of the primary valve 70.

Thus, it will be seen that the primary valve 70 illustrated in FIG. 4 is immediately responsive upon energization of the solenoid 72, but is delayed in operation upon de-energization of the solenoid 72. In this manner, the application of the secondary braking mechanism 45 upon the pinion shaft 15 is delayed upon de-energization of the solenoid valve 65.

FIG. 5 is a schematic view of the electrical circuitry controlling the solenoid valves of the primary and emergency hoist braking mechanisms and the electrical control means for the hoist drum clutches 8 and 9. As shown therein, the drum hoist 10 is in balance with the braking mechanisms applied.

The brake lever til is shown in position preparatory to being actuated to release the primary and secondary braking mechanisms. The brake lever limit switch 81a which electrically connects the brake release solenoid valves 58, 59, 65, and 67 to the input line 82 in its closed position is, thus, open. The brake lever limit switch 8112 which electrically connects the two-position double-acting clutch solenoid valves 83 and 84 to the electrical input line 82 in its closed position is, conversely, closed. Due to this converse relationship between the switches 81a and 81b, furthermore, it will be seen that neither of the solenoid valves 83 and 84 can be energized unless the brake release solenoid valves 58, 59, 65, and 67 are de-energized. In other words, all of the hoist braking mechanisms must be applied before a hoist clutch can be either withdrawn or energized. Furthemore, as the clutch solenoid valves 83 and 84 are each of the two-position, momentary contact type, they will retain the position determined by whichever solenoid was last operated until the operation of the opposing solenoid.

The clutch levers 85 and 86 for the hoist drums A and B, respectively, control the withdrawal and engagement of the clutches 8 and 9. As will be seen from FIG. 5, with both of the clutches 8 and 9 engaged, the clutch lever 85 retains the switch 87 associated with the brake solenoid valve 58 and the switch 88 associated with the engagement portion of the clutch solenoid valve 83 closed, while opening the switch 89 associated with the withdrawal portion of the clutch solenoid valve 83. Similarly, in the illustrated balanced state of the drum hoist 10, the clutch lever 86 maintains the brake and clutch engagement switches 90 and 91, respectively, closed and the clutch withdrawal switch 92 open. In view of the foregoing it will be seen that, when one of the clutch levers 85 and 86 is actuated to withdraw the clutch associated therewith, it opens the switch 87 or Sill associated with the brake release solenoid valve of the hoist drum to be declutched. Thus, the primary braking mechanism on a declutched drum may not be released therefrom prior to the re-engagement of the clutch on said drum. As illustrated, however, both of the clutch engagement switches 83 and 91 are closed such that the hoist It} is in balanced relation and, upon closing the switch 81a, the primary brakes upon both of the drums A and B may be released.

The solenoid valve 67 is adapted to be continuously energized when the switch 81a is closed. The solenoid valve 65 of the emergency braking mechanism 45, however, is controlled in accordance with the clutch switches 93 and 94 and the drum shaft directional switch 95.

More specifically, the clutch switch 93 andthe clutch switch 96 which is associated with the solenoid valve 58 are limit switches and are closed when the clutch 8 on the drum A is fully engaged. The clutch switch 94 and the clutch switch 97 associated with the solenoid valve 59 are limit switches and are closed when the clutch 9 which is on the drum B is fully engaged. Thus, with both of the clutches 8 and 9 engaged, the switches 93 and M are closed and the solenoid valve 65 is energized such that the time delay therein is effective upon deenergiza-tion thereof.

The drum. shaft directional switch is a drag switch which may be driven by either of the shafts 12 or 15 and is arranged such that its contact 95a engages the contact 98 when the load on the hoist drum A is ascending or would be ascending, were its clutch engaged. Similarly, the switch 95 is adapted to have its contact 95a engage the contact 99 when the load on the hoist druim B is ascending or would be ascending, were the clutch 9 engaged. Both of the contacts 98 and 99 open from the contact 95a, however, whenever the speed of the load has been reduced to a low value, thus ensuring that an ascending load cannot slip backwardly after having been brought to rest.

Thus, it will be seen that the solenoid valve 65 is ener gized and its time delay is effective when only the drum A is clutched and the load is ascending and, also, when only the drum B is clutched and the load thereon is ascending. However, when only one of the drums A and B is clutched and the load thereon is descending, it will be seen that the solenoid valve 65 is not energized and the braking mechanism 45 on the pinion shaft is then immediately operative in an emergency.

From the foregoing, it will be seen that the solenoid valve 65 is energized to delay operation of the secondary braking mechanism 45 on the pinion shaft 15 only when both of the drums A and B are operating and the hoist 10 is in balance or when only one of said drums is operating and the load thereon is ascending. Similarly, it will be seen that the present invention is readily applicable to a single drum hoist to delay the operation of the emergency braking mechanism thereon when the hoist is hauling an ascending load. For example, in application with a single drum hoist, the drum shaft directional switch 95 could be employed to ascertain the directional rotation of either the drum shaft or the driving shaft such that the solenoid valve 65 is only energized when the load on the hoist is ascending.

The operation of the device is believed to be apparent from the foregoing description.

From the foregoing it will be seen that the present invention is adaptable for use in many forms of drum hoists, substantially regardless of the number of drums therein included.

From the foregoing it will be seen that I have provided new and improved means for accomplishing all of the objects and advantages of my invention.

Having thus described my invention, 1 claim:

1. A hoist apparatus comprising:

a support;

a shaft mounted for rotation on said support;

motor means operatively connected to said shaft for effecting rotation thereof;

a hoist drum carried by said shaft for rotation therewith;

rope means around said hoist drum and carrying a load thereon, said rope means being wound on said hoist drum to effect movement of said load upon rotation of said hoist drum;

primary braking means operatively connected to said hoist drum for preventing rotation thereof; secondary braking means operatively associated with said hoist drum for preventing rotation thereof; and means operatively connected to said secondary braking means for delaying application thereof until after said hoist drum has been braked by said primary braking means.

2. A hoist apparatus comprising:

a support;

a shaft mounted for rotation on said support;

motor means operatively connected to said shaft for effecting rotation thereof;

a hoist drum carried by said shaft for rotation therewith;

rope means around said hoist drum and carrying a load thereon, said rope means being wound on said hoist drum to effect vertical movement of said load upon rotation of said hoist drum;

primary braking means operatively connected to said hoist drum for preventing rotation thereof; secondary braking means operatively associated with said hoist drum for preventing rotation thereof; and means controlling said secondary braking means to delay application thereof until after said primary brak- 8 ing means have been applied to said hoist drum when said primary and secondary braking means are ac tuted while said hoist drum is raising the load thereon in a vertical direction.

3. A hoist apparatus according to claim 2 wherein said secondary braking delaying means is disabled when said hoist drum is rotating to lower the load in a vertical direction.

4. A hoist apparatus comprising:

a support;

a shaft mounted for rotation on said support:

motor means operatively connected to said shaft for effecting rotation thereof;

a hoist drum carried by said support for rotation with said shaft;

rope means around said hoist drum and carrying a load thereon, said rope means being wound on said hoist drum to effect vertical movement of said load upon rotation of said hoist drum; primary braking means operatively connected to said hoist drum for preventing rotation thereof;

secondary braking means operatively associated with said hoist drum for preventing rotation thereof and normally locking said hoist drum against rotation; and

means for releasing said secondary braking means from said lock-ing of said drum hoist;

said braking release means including means for delaying the application of said secondary braking means until after said hoist drum has been braked by said primary braking means only when said primary and secondary braking means are applied while said hoist drum is rotating to raise the load thereon in a vertical direction.

5. A hoist apparatus according to claim 4 wherein said secondary braking release means comprises fluid operable means urging said secondary braking means from locking relationship with said hoist drum and said secondary brake delaying means comprises valve means interposed in said fluid operable means and retarding the action thereof to apply said secondary braking means into said locking relationship with said drum hoist.

6. A hoist apparatus according to claim 5 wherein said valve means retarding the action of said fluid operable means is automatically actuated to provide such retardation whenever said primary and secondary braking means are applied while the drum hoist is rotating to raise the load thereon in a vertical direction.

7. A hoist apparatus comprising:

a support;

shaft means mounted for rotation on said support;

motor means operatively connected to said shaft means for effecting rotation thereof;

a pair of hoist drums carried by said support;

means for selectively connecting each of said pair of hoist drums to said shaft means for rotation therewith;

rope means wound around each of said hoist drums,

each of said rope means being wound in opposing relation to the other thereof and carrying a load for movement in a vertical direction upon rotation of said hoist drums;

primary braking means operatively connected to said hoist drums for locking such against rotation; secondary braking means operatively associated with said hoist drums for locking such against rotation; and

means controlling said secondary braking means to delay the application thereof until after said hoist drums have been braked by said primary braking means.

8. A hoist apparatus according to claim 7 wherein said control means for delaying the application of said secondary braking means is operable only when one of said hoist drums is rotating with said shaft means to raise a load in a vertical direction.

9. A hoist apparatus according to claim 7 wherein said secondary braking delaying means is disabled when only one of said hoist drums is rotating with said shaft and is lowering a load in a vertical direction.

10. A hoist apparatus comprising:

a support;

shaft means mounted for rotation on said support;

motor means operatively connected to said shaft means for effecting rotation thereof;

a pair of hoist drums carried by said support;

means for selectively connecting each of said pair of hoist drums to said shaft means for rotation therewith; rope means wound around each of said hoist drums, each of said rope means being wound in opposing relation to the other thereof and carrying a load for movement in a vertical direction upon rotation of said hoist drums; primary braking means operatively connected to said hoist drums for locking such against rotation;

secondary braking means operatively connected to said hoist drums and normally locking such against rotation; and

means for releasing said secondary braking means from said h-oist drums to permit rotation thereof;

said braking release means comprising means for delaying the application of said secondary braking means when said primary and secondary braking means are actuated while one of said hoist drums is rotating to move a vertically ascending load until after said primary braking means have been applied to said rotating hoist drum.

11. A hoist apparatus according to claim 10 wherein said secondary braking delaying means is effective only when one of said hoist drums is vertically raising a load.

12. A hoist apparatus according to claim 11 wherein said braking release means comprises fluid operable control means and said braking delaying means comprises valve means in said fluid operable control means and automatically deiaying the action thereof to apply said secondary brake means to said hoist drums.

13. A hoist apparatus according to claim 12 wherein said fluid valve means is automatic in operation and electrically controlled to eflect said delaying action.

14. A hoist apparatus according to claim 13 wherein second shaft means connects said motor means to said shaft means and said secondary braking means locks said second shaft means against rotation to prevent rotation of said hoist drums.

References Cited by the Examiner UNITED STATES PATENTS 3/1951 Crookston 188-105 5/1963 Clarke 188-105 

1. A HOIST APPARATUS COMPRISING: A SUPPORT; A SHAFT MOUNTED FOR ROTATION ON SAID SUPPORT; MOTOR MEANS OPERATIVELY CONNECTED TO SAID SHAFT FOR EFFECTING ROTATION THEREOF; A HOIST DRUM CARRIED BY SAID SHAFT FOR ROTATION THEREWITH; ROPE MEANS AROUND SAID HOIST DRUM AND CARRYING A LOAD THEREON, SAID ROPE MEANS BEING WOUND ON SAID HOIST DRUM TO EFFECT MOVEMENT OF SAID LOAD UPON ROTATION OF SAID HOIST DRUM; PRIMARY BRAKING MEANS OPERATIVELY CONNECTED TO SAID HOIST DRUM FOR PREVENTING ROTATION THEREOF; SECONDARY BRAKING MEANS OPERATIVELY ASSOCIATED WITH SAID HOIST DRUM FOR PREVENTING ROTATION THEREOF; AND MEANS OPERATIVELY CONNECTED TO SAID SECONDARY BRAKING MEANS FOR DELAYING APPLICATION THEREOF UNTIL AFTER 